[PiotrCzapla]

This addresses a warning that iscoroutinefunction has moved to inspect since 3.5 when async def was introduced. Using the asyncio made sense up until Python 3.11 which removes the @asyncio.coroutine decorator the only difference between old asyncio and inspect versions.

Claude note below:
Python 3.14 deprecates asyncio.iscoroutinefunction, and 3.16 removes it, so every call emits a DeprecationWarning. This switches fastcore's three uses to inspect.iscoroutinefunction: is_async_callable (aio), parallel_async_gen (parallel) and flexicache (xtras).

The two return the same result for plain coroutine functions, functools.partial of them and unittest.mock.AsyncMock, checked on Python 3.10, 3.12 and 3.13. The asyncio version also accepted the @asyncio.coroutine decorator, which Python 3.11 removed.

Tests: nbdev-test passes for 03c_aio and 03a_parallel on Python 3.14. 03_xtras stops at an unrelated cell, Person(name="Bob") raising TypeError, which fails the same way on main under 3.14.